The present invention relates to caging systems for laboratory animal care and more particularly to a cage and system which has controlled ventilation, waste containment and cage construction that will direct airflow through the bedding, thus keeping it dry which will reduce bacteria formation caused by humidity and moisture.
Most all existing ventilated rodent cage systems are made with plastic clear solid-bottom cages. Clear cages are used so it is possible to inspect the condition of the inside of the cage without disturbing the animals. The solid bottom of the cage compartment is used to hold bedding material. The cage ensemble generally consists of a metal wire bar lid containing a feed hopper and water bottle capabilities and a plastic top that holds a piece of filter media. The cages are contained in a rack that holds a plurality of cages either single or double sided. An automatic water system introduces water into the cage for the rodent using lixits or water valves located either outside or inside the cage. It must be monitored for proper water pressure and must be flushed periodically. Problems of leakage, high intracage humidity levels and cage flooding are associated with automatic watering systems. Airflow is introduced into the cage either positive or negative pressure in an attempt to rid the cage of harmful contaminants, mainly ammonia and CO2. A plenum, either a separate duct system or made up of components of the rack (i.e. the shelves or the tubing uprights), supply the cage with filtered air through a cage mounted or detached air supply diffuser. Air flow in present designs is either transversely across the cage from the front or rear wall, or, from an inlet in the top of the cage to an outlet in the junction of the top of the cage.
The applicant is aware of the following U.S. patents which are related to cages for laboratory animals:
Fricke U.S. Pat. No. 2,467,525; Fuller et al U.S. Pat. No. 3,063,413; Barney U.S. Pat. No. 3,397,676; Holinan U.S. Pat. No. 3,924,571; Gland et al U.S. Pat. No. 4,085,705; Gass U.S. Pat. No. 4,154,196; Nace 4,201,153; Thomas U.S. Pat. No. 4,402,280; Picard et al U.S. Pat. No. 4,435,194; Sedlacek U.S. Pat. No. 4,480,587; LoMaglio 4,526,133; Spengler 4,528,941; Peters et al 4,798,171; Niki 4,844,018; Spina U.S. Pat. No. 4,869,206; Niki et al U.S. Pat. No. 4,940,017; Sheaffer U.S. Pat. No. 4,989,545; Niki et al U.S. Pat. No. 5,003,022; Niki et al U.S. Pat. No. 5,048,453; Coiro, Sr. et al; U.S. Pat. No. 5,148,766; Coiro, Sr. et al U.S. Pat. No. 5,307,757; Sheaffer et al U.S. Pat. No. 5,311,836; Harr Re 32,113; Semenuk D 351,259; Semenuk D 383,253
Current ventilated caging systems, of which the applicant is aware, for laboratory animal care and use in biomedical research/testing is suboptimal because of the lack of the ability to actually dry the bedding which is the root cause of ammonia gas formation. Present units require 60 or more air changes per hour and have been shown to be ineffective in removing all traces of contaminants. Even small concentrations of ammonia have been shown to cause lesions in the respiratory tracts of mice. In addition, mice are borrowing animals and this behavior leads to prolonged periods with their nasal passages in or very near the bedding which is where the harmful ammonia vapor is forming, and they are burrowing in bedding that can be moisture laden from urination and a leaking water source. Bedding has been deemed as a necessary enrichment for rodents. Present day systems do not address the moisture removal from bedding. Their only attempt to dry the bedding is reduce the cage humidity level by high air change rates in the cage. Due to the high intra-cage ventilation rates required with existing ventilated racks, animal losses can occur due to chilling and dehydration of neonates, hairless and nude strains. While the systems currently in use may provide some biological exclusion, the inability to dry the bedding material, contributes to a lack of animal comfort, and requires an enormous amount of conditioned laboratory air every hour. Filtering air through the bedding attacks the source of ammonia formation whereas other systems only treat the symptoms. By attacking the contamination source, lower amounts of air are required to ventilate the cage effectively. This results in reduced HVAC costs and lower mechanical, electrical and plumbing costs during renovations or new construction due to the smaller system requirements.
In present systems, bedding and nesting materials are placed directly on the floor of the solid-bottom cages, since rodents are nesting and burrowing animals. The primary requirements of bedding materials are: (1) the material must not be harmful to the animal; (2) it must be capable of absorbing moisture without causing dehydration of newborn animals, (3) it must not create excessive dust, (4) it must be economical to use and dispose of. Modern bedding materials are absorbent, but, the fact that the bedding is absorbing moisture allows the formation of urease bacteria which then produces ammonia. A major goal is to direct airflow in the cage in such a manner that it keeps the bedding dry, eliminating the formation of the urease bacteria, thus, creating a better cage environment. Since the harmful contaminants are kept from forming, airflow requirements can be reduced, drastically reducing energy requirements in the lab. Reduced airflow in the cage will also reduce aerosols from bedding dust which reduces the clogging of the cage outlet filter. When cages are operated in a negative pressure for bio-containment purposes, the clogging of the outlet filter could cause the cage to revert to a positive pressure environment which could release cage air into the room. Dry bedding is more easily removed from the cage during change-out periods than wet bedding which can adhere to the cage, making removal difficult and time consuming. Reduced airflow results in lower intra-cage sound levels which could result in less stress on the animal and encourage a more optimum breeding environment. Thus, there is a need for a laboratory animal cage and a system of cages which solve these problems.